This invention relates to a switch for a dynamoelectric machine, and in particular, to a starting switch for a fractional horsepower induction electric motor.
Typically, capacitor start and split phase induction motors have a run winding and a starting or auxiliary winding placed in winding receiving slots provided in the bore of the stator core of the motor. The starting winding is energized during start up of the motor (or when the speed of the motor falls below a specified operating speed) so as to create a rotating field in the stator and to apply sufficient torque to the rotor for starting purposes. Once the motor has accelerated to a desired operating speed (e.g., about 80% or more of the normal operating speed of the motor), the rotor is able to follow the alternations of the magnetic field created by the run windings, and the starting winding is no longer needed and is de-energized. Typically, the starting winding is not intended for continuous use and may fail if not de-energized during normal operation of the motor.
As is conventional, motor starting switches are provided in the motor for energizing the starting winding only during startup of the motor and for de-energizing the starting winding once the motor has attained its desired operating speed. These motor starting switches are generally actuated by a centrifugal actuator mounted on and rotatable with the rotor shaft of the motor. The centrifugal actuator is responsive to the speed of the motor and actuates the starting switch from its start to its run position in response to the motor attaining a predetermined operating speed.
Centrifugal actuators typically include an actuator member movable axially on the rotor shaft from an off or stop position when the motor is stopped (or is operating below a specified operation speed) to a run position when the motor is accelerated to a predetermined operating speed. Typically, an actuator linkage operatively interconnects the motor starting switch and the actuator member of the centrifugal actuator. This linkage may include a lever interconnecting the switch and actuator member, a spring, and means for adjusting the lever with respect to the actuator. In some instances, the lever is pivoted on a portion of the motor itself, for example on the end shield of the motor.
Because the actuator member of the centrifugal actuator moves only a limited distance between its off and run positions, it has heretofore been necessary to accurately adjust the relative positions of the motor starting switch and the centrifugal actuator to ensure that the switch is properly actuated by the centrifugal actuator at a specified motor operating speed. However, relative positions of the actuator and the switch are often accidentally changed when repairs are made upon the motor in the field. Because the tolerances are tight, a slight change in the relative position of the actuator and switch can cause the switch to operate improperly, causing damage to the starting winding. Depending on the direction of misplacement between the actuator and the switch, the starting winding may not be able to be de-energized or the winding may not be initially energized. In the former, the starting winding will run continuously, causing premature failure of the starting winding. In the latter condition, the motor may not be able to be started in the first instance.
It is therefor one object of the present invention to provide a starting switch actuator for a dynamoelectric machine.
Another object is to provide such an actuator in which the clearance between the actuator and the switch is difficult to alter.
Another object is to provide such an actuator that is economical to produce.
These and other objects will become apparent to those skilled in the art upon a review of the following disclosure and accompanying drawings.